At the risk of being called a dang fool, I’m experimenting with sieveing my own ballast for my N scale layout - the ballast being a bucket of prototype pinched from the local ballast bunker. I can get it small enough, but there is a large component of very fine dust to it - too fine. If I could get rid of the dust and just have the remaining slightly larger material I think it would be ideal. I can’t find a sieve to filter out just the dust - everything is too small down there. I feel there must be some way of washing or blowing the dust away.
Do it with water. Place a couple of pounds of the pre-strained stuff spread over the grating/screen, and then run a slow-running hose around and back and forth over the material. Take your time. Do it where all the water won’t become a huge mudhole.
Now, you should see that you will need two screens. One to let the ballast-sized stuff through, as well as the fines, and another below it to catch the ballast, but not the fines.
You’ll have to eyeball it to see what works. You may have to use cheesecloth to let the dusty fines through and retain the ballast grains.
You could try using an old nylon stocking over a vacuum cleaner hose. The nylon will stop the ballast and allow the dust to pass through. We use this to pick up excess ballast when gluing it down on the layout and it works well so long as you don’t use the CFO’s newest expensive hosiery. J.R.